Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$246.76	10.672%	$273.0942	$273.09	$273.10	$273.10
Purchase #2	$40.73	5.221%	$42.8565	$42.86	$42.85	$42.90
Purchase #3	$156.87	6.525%	$167.1058	$167.11	$167.10	$167.10
Purchase #4	$94.42	8.582%	$102.5231	$102.52	$102.50	$102.50
Purchase #5	$32.78	5.530%	$34.5927	$34.59	$34.60	$34.60
Purchase #6	$189.33	6.735%	$202.0814	$202.08	$202.10	$202.10
Purchase #7	$239.65	4.552%	$250.5589	$250.56	$250.55	$250.60
7 purchase totals =	$1,000.54		$1,072.8126	$1,072.81	$1,072.80	$1,072.90